When Apple can release a version of OS X that works, I'll stop recommending a competing OS. Until then, I have no qualms with recommending an OS that actually works.
And so there's no confusion, when I say "works", what I mean is:
- It handles multiple monitors properly.
- It handles email properly. That is to say, mail.app can check for unread emails.
- It is capable of running without crazy lag on non SSD equipped computers.
To date, the last version of OS X that met all three of these (IMO quite reasonable) requirements was Snow Leopard. I'd like to say that I have high hopes for Yosemite, but early signs point to it looking like crap on non-Retina displays.
I don not use multiple monitors so i can't comment on that. The email app has worked perfectly for me since it was introduced and that didn't change on Mavericks. Lion and Mountain Lion does run without "crazy lag" on non-ssd, i have not tried Mavericks since i got a newer computer with only SSD some months before Mavericks was released. The only complaints i have heard about non-retina displays on Yosemite is the font, (which is easily changeable). This might not be known to new users or those that don't know much.